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000
AGPN40 KWNM 210840
MIMPAC

Marine Weather Discussion for N Pacific Ocean
NWS Ocean Prediction Center Washington DC
140 AM PDT Thu Sep 21 2017

.FORECAST DISCUSSION...Major features/winds/seas/significant
.weather for the North Pacific N of 30N and E of 150W.

GOES Water-vapor satellite imagery and lightning data show a
fairly strong upper level trough over the far eastern north
Pacific Ocean early this morning. The trough is moving east and
will likely move inland toward the Rockies later today and
tonight. As the trough moves east, the threat for showers and
thunderstorms will diminished from west to east over mainly
Oregon and northern California offshore waters today into
tonight. Locally gusty winds and rough seas can occur in or near
any of the thunderstorms that occur over the waters. We will
manually add in the shower and thunderstorm chances to the grids
as the available models once again do not appear to be performing
very well regarding the current shower and thunderstorm activity
detected over the region.

Overall, the 00Z models are remaining quite consistent from past
model cycles, and for the most part these models remain in very
good agreement over the region through the weekend into early
next week. For the early morning package, we see no need to alter
the previous grids and forecast too much so we will stay close
to the previous forecast for the early morning package right
through the forecast period, and then populate with the 00Z GFS
10 meter winds to finish up the forecast for days 5-7. We will
make a few manual adjustments to the ongoing grids so that the
early morning OPC forecast fits well with nearby coastal WFO and
TAFB grids. Otherwise, the chance of gales over the offshore
waters will likely remain quite low through the forecast period.
The best chance for gales will occur over the coastal waters near
the northern California and far southern Oregon coasts Sun night
into Mon night as the pressure gradient between high pressure
west of the offshore waters and a coastal trough strengthens. A
cold front will approach the far northwest portion of PZ5 waters
Mon night as low pressure forms along the front to the west and
northwest of the region. Confidence levels are near to above
average over the waters for the next 5 days.

Seas: The latest observations and altimeter data indicates that
the 00Z Wavewatch III and ECMWF WAM models have both initialized
within a foot or two of the data over the region early this
morning. The output from these two wave models appears to be
fairly similar over the offshore waters for the next few days.
We will use a 50/50 blend of the Wavewatch and WAM models for
the early morning package, and continue to manually edit the
wave grid over areas adjacent to the WFO coastal waters and TAFB
forecast areas.

Extratropical Storm Surge Guidance: n/a.

.WARNINGS...Preliminary.

.PZ5 Washington/Oregon Waters...
     None.

.PZ6 California Waters...
     None.

$$

.Forecaster Mills. Ocean Prediction Center.


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